You know Craig, your suggestion about moving the piano lid up and down
to control the volume on my Duo-Art might work. I may have just enough
vacuum to move the lid if I add a counter weight or heavy spring to the
system.  What do you think.

One problem that has been bugging me is about the Duo-Art stack
leakage. There was talk about if the cross values were leaking too much
that this would cause the 0 setting to be adjusted to high.  When
higher vacuum levels are required, this will compress the leather,
reducing the leakage which in turn will make the loud playing even
louder.

When I first measured the zero value of the regulator of 5", I thought
this was great but for the wrong reason.  I thought this was giving me
a general reading that the valve leakage was OK.

I can't decide what this zero reading is really telling me.  It could
give a general indication about how well the piano is regulated, now
tight the spring tension is at the end of each key pneumatics, how
leaky the values are, how leaky the key pneumatics are, and now tightly
the knife values are sealing inside the regulator.  The problem is that
they all affect each other, they all affect the zero setting of the
Duo-Art Regulator and the vacuum readings could still be reading 5
inches of water which is normal but the volume of air that is running
through the regulator is too high or even to low if the stack is too
air tight.

The size of the key pneumatics determine how much weight it can lift
with a given amount of vacuum pressure.  If the system doesn't have any
leaks (meaning air movement inside the closed system is almost
nothing), then this vacuum pressure will be the same at both ends of
the system. This can be seen by placing the vacuum gauge on 2 feet or
25 feet of hose.  The gauge reads the same number if there isn't any
air movement (or leaks) in the hose. This isn't realistic inside the
stack because of the leaking valves but continue with this thought for
a while.

When running the test roll to set the zero adjust, it is only striking
1 key at a time.  The regulator will try to keep the pressure at the
regulator constant whether the stack leaks a little or a lot (within
reason). It doesn't take much vacuum to move only 1 key.

If the stack is fairly air tight, most of this vacuum measured at the
regulator will be delivered to the single pneumatic which will lift the
key at a velocity that will strike the string softly if the sustain
pedal is on.  It does this because I adjusted it by listening, not
measuring with a vacuum gauge.

I now take a vacuum measurement and it reads 5 inches of water on the
hose leading to the regulator. If the stack was perfect, then I would
know that there is 5 inches going to the key pneumatic.  But because of
the leaking valves, it doesn't tell me much.  Only that there is 5
inches at the regulator.

Now much of this vacuum is being delivered to the pneumatic, I don't
have a clue unless I measure it at the pneumatic.  Only a portion of
this vacuum might be reaching the key because of leaks inside the
stack.

Ops, another unrelated brain glitch.  What makes the piano play louder?
I believe that it is related to how hard the hammer (really the
velocity) strikes the string.  The faster the hammer moves, the louder
the note plays.  Does leaking valves change the velocity? probably.
What is the percentage lost when the piano plays soft .vs. loud. I am
sure that you could almost throw away the measured loss when we are
talking about vacuum levels over 10 inches of water.  The loss is more
of a problem when setting the zero adjust and playing softly.  Craig
must have something up his sleeve to measure this leakage.  Would
measuring the vacuum pressure that the key pneumatic at the 0 setting
and the level seen at the regulator indicate how bad the valve leak
problem is?

What if the value gap is set smaller from one piano to the other. This
was brought up a few weeks ago but I can't find the reference. The
vacuum can't move thru the valve that has a smaller gap. The vacuum
moves more slowly out of the pneumatic which slows down the motion
going to the keys (less velocity = less volume).

This may not show up as a problem when playing at low volumes but could
make a big difference when playing the louder passages. When vacuum
levels of 30 inches are asked for, then the piano might play at a much
softer level because the valves are limiting the maximum amount of air
that can be removed from the key pneumatics when the vacuum is applied
to them. This isn't a problem at all.  It helps reduce the volume at
the top end if we are talking about by problem.

Could changing the values seats from Cross to Round also change how
fast the air is allowed to be sucked out of the pneumatic.  I would
think that the newer Round ones would operate more quickly if set to
the same gap as used with the cross valves.

This could be one of the differences between my stack and a completely
rebuilt stack which I am sure that Craig Brougher and maybe others
would be working with. It may not be the total reason why my piano is
louder but could this be contributing to the problem?

If the gaps on the valves are made smaller, how does this affect the
playing volumes with changes in the humidity.  Leather does change
slightly with humidity and with tighter gaps, this change small change
in thickness could be larger than expected.   With high humidity, the
valve gap would get smaller, making the piano play softer.  In dry
winter months when using the heater, the leather shrinks in thickness
which increases the gap and could make the piano play louder.   The
piano action could also aggravate this because of the felt bushings.